Navigational devices have been used with computers and other types of computing systems for many years. A computer mouse is one example of a navigation device. With a mechanical computer mouse, a ball rolls over a mouse pad as the mouse is moved. Interior to the mouse are wheels that contact the ball and covert its rotation into electrical signals representing orthogonal components of motion.
Another type of computer mouse is an optical mouse. FIG. 1 is a diagrammatic illustration of a portion of an optical mouse according to the prior art. Mouse 100 includes light source 102 and imager 104. Light source 102 is typically implemented as a light-emitting diode, which emits light 106 towards surface 108. Imager 104 captures images from surface 108 and transmits the images to processing circuit 110. Processing circuit 110 typically correlates the images in order to track the motion of objects in the images and determine the speed and distance mouse 100 has moved across surface 108.
Contamination in the optical path between surface 108 and imager 104 can reduce the ability of processing circuit 110 to determine motion. Contamination such as dust, lint, and condensation appear as background noise that remains relatively constant from image to image and reduces the efficiency of the correlation engine. If the contamination increases over time, the background noise may cause the correlation engine to produce signals that overwhelm the other signals and cause processing circuit 110 to erroneously conclude optical mouse 100 is not moving.